Question

a conversing mirror forms a real image of height 4cm of an objest of height 1cm placed 20cm away from the mirror calculate image distance and focal length

Answer 1

u = -20 cm
h1 = 1 cm
h2 = - 4 cm
-v/u = h2/h1
-v/-20 = -4/1
-v = -20 x - 4 = 80 cm
v = -80 cm
The object is placed at -80 cm .
1/v + 1/u = 1/f
1/-80 + 1/-20 = 1/f
-1/80 - 1/20 = 1/f
(-1-4)/80 = 1/f
-5/80 = 1/f
1/-16 = 1/f
Focus is located at -16 cm .
Focal length = -16 cm

Answer 2

f= -2.66 cm
hope this helps